Conjunctivitis, also known as pinkeye, is an infection of the outermost layer of the eye, the conjunctiva, the inner surface of the eyelids or both the conjunctiva and the inner surface of the eyelids. Conjunctivitis may be caused by viruses, bacteria, allergens or chemicals. Conjuctival infections can lead to the involvement and inflammation of other parts of the eye including the cornea, sclera, lacrimal glands, meibomian glands and eye lash follicles.
Conjunctivitis caused by pathogens such as viruses (typically adenovirus, herpesvirus, coxsackie virus, pox virus and Epstein Barr virus) and bacteria is transmitted through contact of the eye with infected particles, droplets, contact lenses, medical or ophthalmic equipment. Adenovirus can be transmitted by respiratory droplets from a cough or sneeze of a person who is suffering an adenovirus respiratory infection. Inadequately sterilized contact lenses, medical or ophthalmic instruments may also cause conjunctival infection.
Adenovirus infection may rapidly spread through schools and childcare centres where children come into close contact with each other. In turn, children may infect other members of the family including siblings and parents. Although any microbe can cause inflammation of the outer eye, it has been estimated that up to 92% of diagnoses are due to adenovirus-associated epidemic keratoconjunctivitis (EKC).
Herpes zoster ophthalmicus is also a common complication of chicken pox. Of about 1 million cases of chicken pox diagnosed each year, about 250,000 develop herpes zoster ophthalmicus and half of these patients further develop complications of herpes zoster ophthalmicus.
Herpetic keratoconjunctivitis can result from both primary and recurrent Herpes Simplex Virus-1 (HSV-1) infection in adults and children. HSV-1 is almost universally acquired and is the most common form of corneal blindness in developed countries. Additionally, HSV-2 can result in Herpetic keratoconjunctivitis, primarily in neonates, who contract the infection passing through the birth canal of an infected individual.
Furthermore, not just viruses such as HSV-1, but also bacteria such as Neisseria gonorrhoeae and Chlamydia spp. may infect the eyes of neonates that have been born by passing through the birth canal of an infected mother. Such infection may cause pain and significant conjunctival discharge and left untreated may cause corneal ulceration.
While some instances of viral conjunctivitis resolve within 1 to 6 weeks without treatment, EKC, which is predominantly a result of infection with adenovirus subtypes 8, 19 and/or 37, is extremely contagious and may progress to involve the cornea as well as the conjunctiva. Involvement of the cornea affects short term vision and sometimes long term vision. Visual impairment may persist for months if subepithelial corneal infiltrates (nummuli), containing viral matter, develop. These generally require treatment with corticosteroids for a period of 4 months. EKC may also result in damage to cells responsible for tear production located in the conjunctiva resulting in long term lachrymal difficulties such as dry eye syndrome. EKC quickly spreads through a population, particularly those where large numbers of people are gathered together at close proximity such as in schools, childcare centres, hospitals, elderly care units, doctors' offices, military bases, offices and factories.
In otherwise healthy patients, conjunctivitis may resolve itself over time. However, in immunocompromised or immunosuppressed patients, such as those with HIV or hereditary immunodeficiencies, cancer patients undergoing chemotherapy, solid organ transplant or stem cell transplant recipients, significant infection and life threatening complications may result.
While conjunctivitis, especially viral conjunctivitis, primarily affects one eye, transmission to the other eye is common, particularly considering that an average person involuntarily touches their eyelids and tarsal conjunctiva about 14 times per day and this is increased in those who apply eye cosmetics and/or wear contact lenses.
Conjunctivitis can lead to blurred vision, loss of vision and in some cases pain as well as ongoing dry eye syndrome if loss of tear producing cells occurs.
Conventional therapies for conjunctivitis include topical use of non-steroidal anti-inflammatory medications, antibiotic eye drops or ointments and in severe viral infection topical corticosteroids and/or oral antiviral treatment. However, many of these treatments are not effective or are only moderately effective and need frequent administration or administration within 72 hours of onset of symptoms. Conventional eyedrops also include preservatives that may cause eye irritation in those suffering from conjunctivitis and unpreserved solutions are suitable for one use only or must be refrigerated. Conventional therapies have toxicity profiles that limit their use. Furthermore, there are no effective anti-viral agents available for treating adenoviral conjunctivitis topically. Conventional therapies are also not suitable for prophylactic use and therefore do not reduce or inhibit the spread of infection to the other eye of an individual or in those populations at risk of contracting a conjunctival infection.
Conventional therapies are typically tailored to the type of infection, bacterial or viral and are not suitable for treatment of both viral and bacterial infection simultaneously. However, it is sometimes difficult in practice to distinguish whether a patient has a viral or bacterial infection. Practitioners will treat with antibiotics due to an inability to identify the etiology and the absence of effective low toxicity topical antivirals and consequently there is much unnecessary prescribing of antibiotics. Co-infection with viral and bacterial pathogens also requires multiple therapies to be administered.
The frequency of infection is increased in contact lens wearers due to increased eye contact and the presence of a foreign body. Suspension of contact lens wear is generally required while being treated with conventional therapies as the lens may act as a nidus for the infective agent, irritate the condition and prevent treatments from reaching or remaining on the relevant area of the eye.
Since eye infections such as conjunctivitis result in significant social and economic effects including loss of school days and loss of work days, alternative therapies for treatment and especially the prophylaxis of eye infections such as conjunctivitis are required.